I. Field
The present disclosure relates generally to a process for the separation of mono- and di-carboxylic acid compounds; more specifically, to processes for the separation of at least one mono-carboxylic acid compound from a mixture comprising at least one mono-carboxylic acid compound and at least one di-carboxylic acid compound by selective elution from an ion exchange chromatography medium.
II. Description of Related Art
Crude oil is currently the source of most commodity and specialty organic chemicals. Many of these chemicals are employed in the manufacture of polymers and other materials. Examples include ethylene, propylene, styrene, bisphenol A, terephthalic acid, adipic acid, caprolactam, hexamethylene diamine, adiponitrile, caprolactone, acrylic acid, acrylonitrile, 1,6-hexanediol, 1,3-propanediol, and others. Crude oil is first refined into hydrocarbon intermediates such as ethylene, propylene, benzene, and cyclohexane. These hydrocarbon intermediates are then typically selectively oxidized using various processes to produce the desired chemical. For example, crude oil is refined into cyclohexane which is then selectively oxidized to “KA oil” which is then further oxidized for the production of adipic acid, an important industrial monomer used for the production of nylon 6,6. Many known processes are employed industrially to produce these petrochemicals from precursors found in crude oil. For example, see Ullmann's Encyclopedia of Industrial Chemistry, Wiley 2009 (7th edition), which is incorporated herein by reference.
For many years there has been an interest in using biorenewable materials such as carbohydrates (e.g. glucose derived from starch, cellulose or sucrose) as a feedstock to replace or supplement crude oil. See, for example, Klass, Biomass for Renewable Energy, Fuels, and Chemicals, Academic Press, 1998, which is incorporated herein by reference. Moreover, there have been efforts to produce adipic acid from renewable resources using processes involving a combination of biocatalytic and chemocatalytic processes. See, for example, “Benzene-Free Synthesis of Adipic Acid”, Frost et al. Biotechnol. Prog. 2002, Vol. 18, pp. 201-211, and U.S. Pat. Nos. 4,400,468, and 5,487,987. The conversion of carbohydrates into value-added chemicals generates carboxylic acid compounds, including mono-carboxylic acid compounds and di-carboxylic acid compounds. Separation and purification of the mono-carboxylic acid compounds and di-carboxylic acid compounds is desirable. One technique for separating mono-carboxylic acids from di-carboxylic acids is disclosed in U.S. Pat. No. 6,284,904. The methods disclosed in the '904 patent require use of strong inorganic acids such as H2SO4, HCl, nitric acid, and phosphoric acid. Use of such strong acids in aqueous solution presents a variety of challenges that must be met for commercial viability. Among them are the costs associated with having to employ and handle strong acids, both the need to employ special materials for the separation equipment and to handle the removed separation product containing such acids, and the downstream environmental costs associated with separation of the strong acids from the desired product and disposal of unreuseable spent strong acids. The production of chemicals from polyhydroxyl-containing substrates (e.g., glucaric acid), and especially for the production of chemicals from polyhydroxyl-containing biorenewable materials (e.g., glucose derived from starch, cellulose or sucrose) to important chemical intermediates such as adipic acid have been reported in U.S. Patent App. Pubs. US2010/0317822 and US2010/0317823, both of which are hereby incorporated by reference in their entireties. In US2010/0317823, processes for the conversion of glucose to an adipic acid product via glucaric acid or derivatives thereof are reported. Such processes include the steps of catalytic oxidation of glucose to glucaric acid or derivatives thereof followed by catalytic hydrodeoxygenation of glucaric acid or derivatives thereof to an adipic acid product. The catalytic oxidation step produces glucaric acid and derivatives which are subsequently hydrodeoxygenated to form an adipic acid product. In addition to glucaric acid and derivatives, mono-carboxylic acid intermediates and other di-carboxylic acid side products are formed in the oxidation reaction and some unreacted glucose may be present. The mono-carboxylic acid compounds and unreacted glucose, if separated from the di-carboxylic acid compounds, may be recycled to the oxidation reactor to increase overall yield of the adipic acid product. However, the recycle streams should not contain added components that could adversely affect the oxidation reaction. Moreover, the separated di-carboxylic acid compounds-containing solution that is supplied to the hydrodeoxygenation reaction should not, to the extent possible, impose additional costs to the process by requiring special materials of construction to enable the separation and/or handling of the separated products. Moreover, the supply of the di-acid compounds to the hydrodeoxygenation reaction should not introduce chemicals thereto which can cause the formation of unwanted reaction products which would adversely impact the efficiency and productivity of the reaction and/or adversely impact the downstream processing of the product stream from the hydrodeoxygenation reaction. Thus, there remains a need for processes for the separation of mono- and di-carboxylic acid compounds which avoids the potential adverse impact of employing strong acids.